Saturated fatty acids are long-chain aliphatic carboxylic acids with linear hydrocarbon chains having an even number of carbon atoms, usually C12-C20. Unsaturated fatty acids contain one or more double bonds, the first usually at carbon number 9. Fatty acids are stored in the form of triacylglycerols. Triacylglycerols serve three basic functions: (1) they are the storage forms of carbon and energy in adipose tissue; (2) they form lipoprotein particles which transport ingested fatty acids; and (3) they provide physical protection and thermal insulation for body organs.
Many epidemiological, clinical, and animal studies have indicated that high levels of dietary fat, especially saturated fat, lead to an increase in blood cholesterol levels and increased risk for atherosclerosis. The risk for coronary artery disease can be predicted directly from serum cholesterol levels. Saturated fatty acids are directly responsible for increasing serum cholesterol levels. A diet that minimizes cardiovascular risk factors and contributes to an overall reduction of diseases not cardiovascular in nature, such as diabetes, could be achieved by changing the dietary fat or mix of fatty acids in the diet. Plasma cholesterol levels tend to respond more to reducing saturated fatty acids than to reducing total fat intake, and plasma cholesterol reduction can be achieved with saturated fatty substituents such as monounsaturated or polyunsaturated fatty acids. Both mono- and polyunsaturated fatty acids affect cardiac risk by lowering low density lipoprotein cholesterol levels. Likewise, in many non-insulin-dependent diabetes mellitus patients, the reduction of dietary saturated fat helps lower plasma cholesterol levels and reduce the risk for coronary heart disease.
Conjugated linoleic acids (CLAs) are a group of 18 carbon FAs that have two double bonds, with positional and geometric variations around the 9, 10, 11 and 12 carbon positions. Dietarily they are principally derived from ruminant animals in meat and dairy products, as they occur only in trace amounts in plants. Considerable work has been carried out in experimental systems and animal models indicating that CLAs, principally the C 18:2 cis9 trans11 form, play a considerable role in a number of areas affecting human health. CLAs have been shown to be anti-carcinogenic and anti-athersclerosis, as well as helping to reduce severe wasting (cachexia) associated with cancer. Other studies, in a variety of animal species, have shown that CLAs can promote lean body growth, increase feed efficiency and decrease fat accumulation. Furthermore, several studies suggest that CLAs can modulate the immune response and thus reduce the cachetic response, enhance cell-mediated responses, and decrease the inflammatory response.
Approximately one third of saturated fatty acids in American diets comes from the consumption of dairy products, and approximately one quarter of saturated fatty acids in the diet are supplied by the consumption of meat. Problems associated with control of intake of saturated fatty acids include consumer compliance, with consumers generally favoring foods that have a higher content of saturated fatty acids.
There is a need in the art for food products that have lower levels of saturated fatty acids. The present invention addresses this need by providing transgenic animals that make food products (e.g., milk, meat, and eggs) having lower levels of saturated fatty acids.
Literature
U.S. Pat. No. 6,432,684; Maga and Murray (1995) Bio/Technol. 13:1452-1457; Strittmatter et al. (1974) Proc. Natl. Acad. Sci. USA 71:4565-4569; van Berkel et al. (2002) Nat. Biotechnol. 20:484-487; U.S. Pat. Nos. 6,432,469, 6,410,761, and 6,333,353.